Two Dimensional Arrays

General TIPS

• If the question is a ROW question start with the for-loop for the row.
• If the question is a COLUMN question start with the for-loop for the column.
• When adding or deleting from a 2D array it is important to clear the string grid first. One can use a counter in the for-loop but if your ColCount / RowCount was set to be higher than the counter for totals and averages, you will not be clearing those cells.

for k := 0 to stgOutput.ColCount do

stgOutput.Cols[k].Clear;

for k := 0 to stgOutput.RowCount do

stgOutput.Rows[k].Clear;

• NEVER use the string grid to process / store data, A string grid should only be used for output. For example: if stgOutput.Cells[iCol,iRow] = 'John' then is not allowed and will cause the learner to lose marks for not using the array. The learner needs to use the array if arrName[iRow,iCol] = 'John' then
• Remember that in an array the row goes first. Easy to remember since array has an R for Row. For example: stgOutput.Cells[iCol,iRow] := arrName[iRow,iCol];
• To display in a string grid you need to place the column first. Easy to remember as the string grid has a .Cells property that starts with a C for column. For example: stgOutput.Cells[iCol,iRow] := arrName[iRow,iCol];
• I know in the past some teachers showed their learners that you could swap the rows and columns around in the array. This only works for some of the solutions but due to more recent papers, where 2D arrays have been given with a parallel 1D array in the declaration of the programs, this will no longer be possible.
• What should they be able to do?
  1. Determine the highest, lowest, total and average of the entire array
  2. Determine the highest, lowest, total and average of each row or each column.
  3. Delete a row or a columns.
• Two dimensional arrays are mostly asked in the last question but have also been included in the OOP question.

Sorting 2D arrays

I could think of two ways that learners could be asked to sort 2D arrays.

Sorting according to the parallel one-dimensional array.

For example: If you have a one-dimensional array containing names and a 2D array containing there marks over 4 terms and you need to sort them alphabetically.

• It is important to remember that your if-statement, contains the condition according to which you need to sort the array.
• You will use the same method as sorting one-dimensional arrays, but you will add code to also swap the rows in the 2D array keeping the columns the same.

Sorting according to a specific column in the 2D array.

For Example: If you are asked to sort the array according to the first mark (i.e. Column) of the 2D array.

• The code will look the same as above but you will change the if-statement condition, to sort according to the first column of your 2D array.

Sorting each rows's data

For Example: Sorting the marks of each learner from lowest to highest